Magnetic chip detector and method of use

ABSTRACT

A gas turbine engine can have a magnetic chip detector system with a first conductor member and a second conductor member both exposed to a lubricant flow path of the gas turbine engine, at least a first one of the conductor members including an electromagnet including a coil wrapped around a ferromagnetic core. As part of an engine shutdown procedure, an intrinsic magnetic field strength within the ferromagnetic core can be increased by circulating electrical current in the coil, and the electrical current circulation can then be interrupted for the magnetic field to remain active during engine shutdown.

CROSS-REFERENCE TO RELATED APPLICATION

The application is a continuation in part of U.S. application Ser. No. 16/799,282 filed on Feb. 24, 2020 by applicant, the contents of which are hereby incorporated by reference.

TECHNICAL FIELD

The application relates generally to gas turbine engines and, more particularly, to systems for detecting metallic particles in a liquid flow therein.

BACKGROUND OF THE ART

The presence of metallic particles in a liquid flow in an engine, such as the oil flow or coolant flow, for instance, can be an indication of component wear, malfunction, or impending failure, this can be the case for components such as engine gears or bearings for instance. To this end, metal particle detectors have been used to detect the presence of such metallic particles. While known metal particle detectors have been satisfactory to a certain degree, there always remains room for improvement. For instance, some metal particle detectors use magnetic attraction provided by active magnetic fields emitted by electromagnets. While the use of electromagnets can be advantageous in terms of confirming chip detection, for instance, they are typically not powered when the engine is not in operation, and therefore may not retain attracted chips.

SUMMARY

In one aspect, there is provided a method of operating a magnetic chip detector system integrated within a gas turbine engine, the magnetic chip detector system having a first conductor member and a second conductor member both exposed to a lubricant flow path of the gas turbine engine, at least a first one of the conductor members including an electromagnet including a coil wrapped around a ferromagnetic core, the method comprising: performing an engine shutdown procedure including increasing an intrinsic magnetic field strength within the ferromagnetic core including circulating electrical current in the coil; and interrupting the electrical current circulation in the coil for an engine shut-down period of time during which the intrinsic magnetic field strength remains in the ferromagnetic core.

In another aspect, there is provided a method of operating a magnetic chip detector system having a first conductor member and a second conductor member both exposed to a liquid flow path and separated from one another by gap, each one of the conductor members having a magnetic field oriented into the liquid flow path, at least a first one of the conductor members including an electromagnet including a coil wrapped around a ferromagnetic core in a manner for the corresponding magnetic field to be actively modifiable via control of electrical current in the coil; an electrical energy source configured to induce a current circulation across the gap; and a meter configured to measure a response of the gap to the induced current circulation, the method comprising: increasing an intrinsic magnetic field strength within the ferromagnetic core including circulating electrical current in the coil; and interrupting the electrical current circulation in the coil for a period of time during which the intrinsic magnetic field strength remains in the ferromagnetic core.

In accordance with another aspect, there is provided a gas turbine engine comprising a magnetic chip detector system having a first conductor member and a second conductor member both exposed to a liquid flow path and separated from one another by gap, each one of the conductor members having a magnetic field oriented into the liquid flow path, at least a first one of said conductor members having an electromagnet including a coil wrapped around a ferromagnetic core; an electrical energy source configured to induce a current circulation across the gap; a meter configured to measure a response of the gap to the induced current circulation, and a capacitor operatively connected to the coil in a manner to charge as electrical energy is supplied to the coil, and to discharge in a manner to generate a current pulse into the coil at engine shutdown.

DESCRIPTION OF THE DRAWINGS

Reference is now made to the accompanying figures in which:

FIG. 1 is a schematic cross-sectional view of a gas turbine engine;

FIG. 2A and FIG. 2B are a first embodiment of a magnetic chip detector showing a sequence of two steps in accordance with one possible method of use;

FIGS. 3A-3C show a sequence of steps of another example method of use of the embodiment shown in FIGS. 2A and 2B, addressing the collection of small metallic particles and FIG. 3D is a variant of FIG. 3B;

FIGS. 4A-4C show a sequence of steps of another example method of use of the embodiment shown in FIGS. 2A and 2B, addressing the collection of a metallic chip above a given size, and FIG. 4D is a variant of FIG. 4B;

FIG. 5 shows a second embodiment of a magnetic chip detector;

FIG. 6 shows current amplitude variation in alternating current, in accordance with one possible method of driving the coils in the embodiment of FIG. 5;

FIG. 7 shows another embodiment of a magnetic chip;

FIG. 8A shows a first embodiment of the electromagnet design which can be used as an active magnetic field conductor member in embodiments of a magnetic chip detector, comprising a coil wrapped around a permanent magnet;

FIG. 8B shows a second embodiment of the electromagnet design which can be used as an active magnetic field conductor member in embodiments of a magnetic chip detector, comprising a coil wrapped around a ferromagnetic core;

FIG. 8C shows a third embodiment of the electromagnet design which can be used as an active magnetic field conductor member in embodiments of a magnetic chip detector, comprising a coil wrapped around a ferromagnetic and a permanent magnet;

FIG. 9 shows another embodiment of a magnetic chip detector using active magnetic field conductor members in accordance with the embodiment of FIG. 8A;

FIG. 10 shows an example hysteresis loop for a method of using an active magnetic field conductor member having an intrinsic permanent magnetic field;

FIG. 11 shows another embodiment of a magnetic chip detector; and

FIG. 12 shows another embodiment of a magnetic chip detector;

FIG. 13 is a schematic showing one embodiment where a capacitor is used to generate a current pulse.

DETAILED DESCRIPTION

FIG. 1 illustrated a gas turbine engine 10 of a type preferably provided for use in subsonic flight, generally comprising in serial flow communication a fan 12 through which ambient air is propelled, a compressor section 14 for pressurizing the air, a combustor 16 in which the compressed air is mixed with fuel and ignited for generating an annular stream of hot combustion gases, and a turbine section 18 for extracting energy from the combustion gases.

The compressor 14, fan 12 and turbine 18 have rotating components which can be mounted on one or more shafts. Bearings 20 are used to provide smooth relative rotation between a shaft and casing (non-rotating component), and/or between two shafts which rotate at different speeds. An oil lubrication system 22 including an oil pump 24, sometimes referred to as a main pump, and a network of conduits and nozzles 26, is provided to feed the bearings 20 with oil. Seals 28 are used to contain the oil. A scavenge system 30 having cavities 32, conduits 34, and one or more scavenge pumps 36, is used to recover the oil, which can be in the form of an oil foam at that stage, from the bearings 20. Oil conduits are also use to and from gearing, and/or to and from auxiliary components, for instance. It is relatively typical to use one or more air-oil separator and one or more filter between the scavenge system 30 and the nozzles 26 to control the quality of the lubricant being supplied to the bearings.

The presence of metallic chips in the scavenge system 30 can be an early indication of component wear or even component failure. Accordingly, it can be desired to provide a chip detector 40 in the scavenge system 30. A single chip detector 40 may be used, which may be located immediately upstream of the scavenge pump 36 or filter(s) for instance, or multiple chip detectors can be used, e.g. in a main scavenge line, in a plurality of scavenge line segments forming part of a scavenge line network, etc.

To detect metallic chips of ferromagnetic materials such as iron, cobalt, nickel and some associated alloys (e.g. steel), a magnetic chip detector 40 can be used.

A first example of such a magnetic chip detector 40 is presented in FIGS. 2A and 2B. This magnetic chip detector 40 includes two conductor members 44, 46, which can be exposed to a flow 41 in the fluid path 42 (here a scavenge oil path), and separated from one another by a gap 48 of non-conductive material (e.g. electrical insulator) having a given width. The conductor members 44, 46 can be prongs or discs of electrically conductive material to name two possible examples. As will be seen in greater detail below, active or passive magnetic fields can be associated to the conductor members, and therefore, it will be understood that the conductor members can be permanent magnets, have permanent magnets (e.g. magnetized hard ferromagnetic core) included within a body, or simply be a non-magnetic material (e.g. soft ferromagnetic core) surrounded by a coil, to name some examples.

The conductor members 44, 46 can be individually held with a tip 45, 47 exposed to the lubricant path 42, in sockets of non-conductive material, for instance, or collectively held in a body of electrically insulating material such as plastic, which itself serves as a plug configured to be received in a corresponding socket, to name another possible example. The conductor members 44, 46 can be permanently embedded into a non-conductive material, such as by being overmoulded by non-conductive material, which may be a non-conductive material of the scavenge oil line, to name yet another example. Numerous variants are possible and the details can be selected as a function of the specificities of a targeted implementation. The conductor members 44, 46 can be said to have axes associated with an orientation of the magnetic fields, oriented towards/into the fluid path 42. An electrical energy source 50 is provided and configured in a manner to allow inducing a current along a circuit path 52 extending from one of the conductor members 44 to the other 46 across the fluid path 42, and a meter (not shown) is provided to measure a response of the circuit path 52 to the induced current. The purpose and use of these two latter components will be detailed below.

The magnetic chip detector 40 is further configured in a manner to allow magnetic fields to be emitted in general alignment with the axes of the conductor members 44, 46. At least one of the magnetic fields is active, in the sense that it can be controllably modified. In the example presented in FIGS. 2A and 2B, a second one of the magnetic fields is passive, and imparted here by means of using a second conductor 46 in the form of a permanent magnet 54, whereas the first magnetic field is active, and imparted here by means of using an electromagnet 56, and more specifically by circulating current along a coil 58 wrapped around a conductive core. In alternate embodiments, two active fields can be used for instance. There are different ways to achieve an active magnetic field, and in other embodiments, both the magnetic fields can be active. Several example variants will be presented below.

The magnetic chip detector 40 can have numerous potential control schemes. A relatively simple first one will now be described with reference to FIGS. 2A and 2B. In a first step, shown in FIG. 2A, a magnetic field is emitted in coincidence with the second conductor member 46, which is achieved here via the permanent magnet 54 material of the conductor member 46. A first pole 62 of a chip 60 of ferromagnetic material is pulled into continued contact with the second conductor member 46 via the magnetic force exerted by the interaction between the magnetic field and the ferromagnetic material. This force can be stronger than any contrary force which may be exerted onto the chip 60, such as a force resulting from the viscosity of the fluid 66 circulating in the fluid path 42 against the chip 40, and which may tend to pull the chip 40 away from the second conductor member 46.

In the first step, the magnetic field around the first conductor member 44 can be nil, or otherwise insufficient to pull the opposite pole 62 of the chip 40 against it (e.g. the field may be of the opposite polarity/orientation but of lesser amplitude than the field emitted around the second conductor member 46, or of the same polarity/orientation, for instance). In the electrical circuit path 52 from the tip 45 of the first conductor member 44 to the second conductor member 46, there is a significant electrical barrier formed by the presence of the fluid 66, which has an electrical conductivity significantly lower than the electrical conductivity of the conductor members 44, 46 and of the chip 60. The electrical circuit path 52 extending from the first conductor 44 to the second conductor 46 across the fluid circulation area is thus open.

Electrical conductors typically have a resistivity value orders of magnitude less than 1 Ω·m (e.g. iron, a good conductor, has a resistivity of 9.7×10⁻⁸ Ω·m, and ferromagnetic materials are typically good conductors), whereas electrical insulators typically have a resistivity value orders of magnitude more than 1 Ω·m (e.g. hard rubber, a good insulator, has a resistivity in the order of 10¹³ Ω·m), and it is therefore quite straightforward for a person having ordinary skill in the art to discern one from the other. Engine oil is typically a good electrical insulator, and can have conductivity values of less than 10 pS/m, for instance, and a wall of oil can thus be very efficient in opening an electrical circuit.

In a second step, while the magnetic field around the second conductor member 46 is maintained, maintaining the electrical contact with the corresponding pole 62 of the chip 60, the amplitude of the magnetic field around the first conductor member 44 is increased in the orientation opposite to the magnetic field around the second conductor member 46 until reaching at least a level of amplitude at which the magnetic force between the first conductor member 44 and the corresponding, opposite pole 64 of the chip 60 overcomes any other existing force and brings the opposite side of the chip 60 into electrical contact with the first conductor member 44. Here, the chip 60 acts as a switch and closes the electrical circuit 52 between the two conductor members 44, 46, across the fluid path 42. This can be achieved in this example by applying electrical energy to circulate electrical current 59 along the coil 58 to activate the electromagnet 56. If electrical current 59 was already circulated along the coil 58, its magnitude can be increased in a scenario where it was of anti-parallel orientation, or its orientation can be reversed in a scenario where it was previously of parallel orientation, to name two examples, all of which will generally be considered as increasing the strength of the magnetic field in an orientation opposite to the orientation of the field across the second conductor member 46 for the purpose of this specification.

The presence of the chip 60 can be detected at this stage by obtaining an indication of the response of the circuit path 52 extending from one conductor member 44 to the other 46 across the fluid path 42 to an induced current circulation, such as via the measurement of the resistivity of the circuit path for instance. Indeed, the resistivity will be significantly lower if a conductive chip 60 is closing the circuit 52, than if a wall of non-conductive fluid 66 is opening the circuit 52. Various means can be used to obtain an indication of the resistivity of that circuit 52 segment. For instance, a difference of potential can be applied across the conductors 44, 46, and the resulting amplitude of electrical current can be measured and compared to a reference value. The reference value can be a predetermined threshold value, for instance, or a value associated to a certain, relatively sudden, change from an earlier-measured value (associated to an absence of a chip 60), to name two examples.

Due to the relationship of V=RI, various alternative ways of measuring the response of the circuit 52 are possible, and these alternative ways will typically involve inducing an electric current across the circuit 52 segment in one form or another. The comparison can be based on electronic hardware, logic gates, and/or involve functionalities provided by a computer, to name some examples, and can use techniques formerly known in the art.

Once the response of the circuit 52 segment to the induced current has been associated to a presence of a chip 60, a suitable indication can be triggered. If the magnetic chip detector 40 is used in an engine of an aircraft 10, for instance, a visual indicator or an audible alarm can be displayed in the cockpit. The visual indicator can be in the form of an icon on a display screen, or of a light which becomes turned on, for instance. The association between the response of the circuit 52 segment and the absence of a chip 60 can be positively indicated, or alternately, an indicator of chip 60 presence can simply be de-activated unless a chip 60 is positively identified. In this specific embodiment, a bridge resistance 68 is used between electrical contacts leading to the two conductor members 44, 46, but such a configuration is optional.

As represented in FIG. 3, in a context where magnetic fields of opposite orientations are sustained around the first conductor member 44 and the second conductor member 46, respectively, for a long period of time, small ferromagnetic particles 70 carried in the fluid flow 41 may be pulled into contact with both conductor members 44, 46, and pile onto one another until they eventually amalgamate, aligning along the magnetic field lines 72, into a bridge 74 which closes the electrical circuit 52 segment between the exposed tips 45, 47 of the conductor members 44, 46. Such small ferromagnetic particles 70 may result from normal wear, and not be a cause of alarm. Obtaining an indication of resistivity along that circuit 52 segment, at that time, may lead to falsely concluding to the alarming presence of the a chip 60, and therefore direct the aircraft to engine 10 check/premature maintenance, whereas the alarm simply resulted from normal wear and the engine 10 was not yet to be performed maintenance upon. This can be a cause of undesired maintenance costs. Such a situation can be avoided by performing a method such as described above in relation with FIGS. 2A and 2B, which can involve preceding the period of monitoring circuit 52 segment response with a period where the actively controlled magnetic field(s) are controlled in a manner to avoid the formation of such a bridge 74.

Accordingly, in one embodiment, it can be desired to intermittently operate the chip detector 40 in a chip attraction mode, during which it can magnetically attract a chip 60 while avoiding smaller particles 70 (e.g. in the configuration of FIG. 2A), and in a chip diagnostic mode, during which it can forcefully bridge the gap with any attracted chip 60, and detect the presence of the chip 60 via the exhibited electrical resistance (e.g. configuration of FIG. 2B). Henceforth, one mode of operation can include regularly alternating between these two modes of operation. Moreover, given principles of electromagnetism which will be detailed below, to break a bridge formed of smaller particles such as fuzz, one may wish to vary one or both of the two magnetic fields.

It will be noted that once a chip has been caught into contact with the two conductor members in a manner that it bridges the electrical circuit between the two conductor members, reducing the strength of one of the fields in a manner sufficient to break a bridge which would have consisted of fuzz, may not cause a larger chip to open the circuit, given the retention force offered by the other conductor member. Accordingly, simply continuing to detect the presence of an electrical current across the gap while the electromagnetic fields are being operated in a manner which is incompatible with the formation of a fuzz bridge across the gap may provide a suitable indication that a chip, and not fuzz, is present in the liquid flow path.

The chip detector 40 can even be designed in a manner to specifically detect only chips 60 above a certain size. One possible way to achieve this is to select a gap 48 width between the conductor members 44, 46 as a function of the desired minimum chip 60 size. The gap width can be of between 0.020″ and 0.060″ in some embodiments, for instance, more specifically of between 0.030 and 0.050″ in some embodiments, and can be specifically of roughly 0.040″ in some embodiments.

In another mode of operation, the chip detector 40 can be used first in a first configuration (e.g. such as FIG. 2B) where it may attract either chips 60 or particles 70 (aka fuzz), and upon detecting a possible chip 60 presence via the resistivity of the circuit 52 segment, the chip detector 40 can be switched to a mode such as shown in FIG. 2A, to flush smaller particles 70 or fuzz with the lubricant flow 41 while continuing the attraction of any chip 60 to the conductor members 44, 46, and then switched back to a configuration such as FIG. 2B, to either confirm or cancel the earlier determination of chip detection. Several other modes of operation are possible, some of which will be described below, but some relevant theory will first be discussed.

Principle 1:

The force between a magnet and a ferromagnetic object is inversely proportional to the distance between them. This means that a strong magnetic field is initially required to attract distant chips 60 flowing in oil 66, but once the chips 60 are attracted to the prong, the magnetic force required to keep them attached is much less since the distance between the chip 60 and the prong is effectively zero. Therefore, a large chip 60 can still be attached to either or both prongs when one field is turned off or reversed, because the field of the other prong holds the chip 60 firmly. The force between two magnets is given by the following equation.

$F = \frac{\mu\; q_{m\; 1}q_{m\; 2}}{4\pi\; r^{2}}$

where

-   -   F is force (SI unit: newton)     -   q_(m1) and q_(m2) are the magnitudes of magnetic poles (SI unit:         ampere-meter)     -   μ is the permeability of the intervening medium (SI unit: tesla         meter per ampere, henry per meter or newton per ampere squared)     -   r is the separation (SI unit: meter).

Principle 2:

When the fields of both prongs point to the same direction, they repel each other. As a result, any small chips/fuzz 70 adjacent to each other that are bridging 74 the gap 48 between the prongs, will separate, resulting in an open circuit. However, large chips 60 bridging the gap 48 may continue to be retained.

Principle 3:

A single large ferromagnetic chip 60 bridging the gap 48 between two prongs is more strongly attracted than multiple smaller chips 70 (fuzz) magnetically attracted together in the presence of the magnetic field between the prongs. This is because multiple ferromagnetic chips 70 introduce multiple boundaries or air (oil) gaps between themselves and between them and the prongs, thus weakening the magnetic flux through them, while a single chip 60 only has two air (oil) gaps. In FIG. 3, darker color is used to represent particles 70 which are more strongly attracted.

The embodiment shown in FIG. 2A can be considered a four pin, single coil, electromagnet 56 & permanent magnet 54 conductor member design. In this specific embodiment, the conductor members 44, 46 are prongs. A single coil 58 is wrapped around a ferromagnetic core 76 to form an electromagnetic prong. When the electromagnet 56 is activated, it generates a field opposite that of the permanent magnet 54 prong. A voltage or current can be applied to IND+ & IND− and the impedance between these points can be measured. As ferromagnetic debris is collected between the prongs 44, 46, the measured impedance will change resulting in a chip 60 indication. The optional resistor 68 can be used to detect dormant failures. When the engine is shutoff, any collected debris will remain attracted to the prongs 44, 46 because the field of the permanent magnet 54 is still active. The electromagnet 56 has a control coil 58 wound around it to control its magnetic field strength and direction by varying the applied current 59. Table 1 below represents different potential states:

TABLE 1 example potential states of a two conductor member design where one conductor member has an active magnetic field and the other one has a passive magnetic field Prong 1 Prong 1 Prong 2 State Current Field Field Effect Chip Positive N-S S-N Attract chips between prongs Detector (Opposite field) OFF Off Nil or S-N Attracted chips weakly attached to probe residual 1, Small chips are shed from probe 1. N-S Chips firmly attached to probe 2. Opposing Negative S-N S-N Small chips bridging the gap repel each (Similar other and break the gap. Large chips still field) bridge the gap.

As presented above, methods of operation may use only the two first states presented in Table 1. For instance, the detector can begin by being used in the OFF state, and the detector can check whether a chip 60 is present by switching to the chip detector state, which can be done once, intermittently, sporadically, or at a predetermined moment in time, for instance. Another method of operation using the two first states can operate in the chip detector state, and upon detecting the presence of ferromagnetic debris, switch to the OFF state, and then back to the chip detector state to obtain a first degree indication that the detection is actually a chip 60, and not just particles/fuzz 70. Such a sequence of operation is illustrated in FIGS. 3A to 40, with FIGS. 3A to 3C showing the detection of particles/fuzz 70, and FIGS. 4A to 4C showing the confirmation of the detection of a chip 60.

Another possible mode of operation which can use the same hardware would be to go further and instead of just using the first two states, it can move to the third state (opposing fields) of Table 1 before returning to the second state (OFF) and then the first state. This is illustrated in FIGS. 3D and 4D. The third state may more efficiently rid the prongs 44, 46 of fuzz/small particles 70 (i.e. require less external drag force from the fluid 66) than the second state, because in the third state, any small particle 70 bridging the gap 48 will become polarized in a manner to repel each other. It will be noted that the application of current from one prong 44 to the other 46 in order to detect the reaction of the area between the prongs 44, 46 can be performed sporadically, in predetermined situations (e.g. in specific states), or permanently (e.g. throughout the different states), to name some examples. The exact choice of method is left to the designer in view of specific contexts.

More states are possible if two active conductor members are used. FIG. 5 shows one such possible embodiment where both conductor members 44, 46 are prongs in the form of electromagnets 56 a, 56 b, each one having a control coil 58 wound around a ferromagnetic core 76 to control its magnetic field strength and direction by varying the applied current 59. Each electromagnet 56 a, 56 b is electrically connected to a detection circuit 52 that can be activated, for instance, when a chip 60 bridges the gap 48 between them.

Each electromagnet 56 a, 56 b can be activated independently and can, for instance, be used in accordance with a method of operation such as one presented above. One notable difference is that if the power to electromagnets 56 a, 56 b is shut down at engine shut down, the magnetic field will significantly diminish, and can leave a weak residual magnetic field which may or may not be negligible. Some of the collected debris may be lost, while some other may remain. If hard magnetic material is used for the prong core 76, then the residual field will be strong. If soft magnetic material is used, then the residual field will be weak.

It will be noted that an embodiment having two active conductor members 44, 46 can further allow additional states, such as prong two off or prong 2 N-S. Accordingly, a possible more elaborated method of operation can be as presented in table 2.

TABLE 2 example method of operation with two active magnetic field conductor members Step Prong 1 Prong 2 Effect 0 N-S S-N Chip Detector Active. Small and large chips are attracted to bridge the gap 1 OFF S-N Small chips shed from P1. Large chips bridging gap still attached to P2 2 S-N S-N Any small chips bridging gap repel each other 3 S-N OFF Small chips shed from P2. Large chips bridging gap still attached to P1 4 S-N N-S Chip Detector Active. Small and large chips are attracted to bridge the gap 5 OFF N-S Small chips shed from P1. Large chips bridging gap still attached to P2 6 N-S N-S Any small chips bridging gap repel each other 7 N-S OFF Small chips shed from P2. Large chips bridging gap still attached to P1 8 N-S S-N Chip Detector Active. Small and large chips are attracted to bridge the gap

By turning off (or weakening the field) and reversing the polarity of one prong at a time, any small chips 70 that are not directly adjacent to the prongs (small chips adjacent to other smaller chips to form a bridge 74) can separate, breaking the bridge 74 between the prongs. Small chips 70 may also be released in the oil flow 41. However, large chips 60 that are adjacent to either prong will remain attached to the prong with the active field.

One possible method of operation embodying the method of Table 2 is to apply coil control current 59 in the form of discrete, square waves. Another one is to apply alternating current 78, such as presented in FIG. 6 for instance. The application of alternating current 78 can alternate the field directions and strengths between the prongs. A designer, with a view of a specific context, may wish to adapt frequency, waveform, and/or phasing angle with a view of attracting a certain size or type of chip 60 while rejecting others on a continuous basis.

A variant of the embodiment shown in FIG. 5 is presented in FIG. 7, where the coils 58 of both prongs are on the same electrical circuit 80, but in an opposite orientation, allowing example states presented in Table 3.

TABLE 3 example states achievable with coils of two active magnetic field conductor members on same circuit Probe Probe 1 Probe 2 State Current Field Field Effect Chip Detector Positive N-S S-N Attract chips between prongs (Opposite field) OFF Off Nil or Nil or Attracted chips weakly attached residual residual or fall off N-S S-N Reverse Negative S-N N-S Small chips bridging the gap repel each other and break the gap

Such an actively controlled chip detector 40 can have two electromagnets 56 a, 56 b; both electromagnets 56 a, 56 b sharing a control coil 58 wound around each one sequentially but in opposite direction to control their magnetic field strength and direction by varying the applied current 59. Each electromagnet 56 a, 56 b can be electrically connected to a detection circuit 52 that is activated when a measurement is taken. This chip detector 40 can be considered a 4 pin design. The coil 58 is wound in opposite directions such that applied current 59 to IN+ & IN− produces a North-South field in one prong and a South-North field in the other prong. The number of turns, or the diameter of the coil 58, may be different between each prong, thus producing unequal field strengths, or the same. As ferromagnetic debris is collected between the prongs, the measured impedance will change resulting in a chip 60 indication. The power to the electromagnets 56 a, 56 b can be turned off for prolonged periods, during which some of the collected debris may be lost, while some other may remain due to the weak residual magnetic field. For this design, when current 59 is turned off, the magnetic fields of both prongs can be eliminated simultaneously (or small residual field is present) since they share the same coil 58, in which case it may be difficult to reverse the field without losing large chips 60. In such a scenario, it can be preferred to reduce the field and strengthen it again.

FIG. 8B presents an active electromagnet design such as presented above, whereas FIGS. 8A and 80 present two example alternate, active electro-permanent magnet designs using a hybrid approach, with a combination of an intrinsic permanent magnetic field and electromagnetic field. The prong of FIG. 8B only attracts ferromagnetic chips 60 when current is applied to the coil 58. If the current is applied in one direction, it will produce a North-South electromagnet, if it is applied in the opposite direction it will produce a South-North electromagnet. The operation can switch between a given amplitude, negative and/or positive, and zero, or be tuned progressively such as to reduce and then re-augment the amplitude. At zero current, a residual field may be present. Depending on the details, collected chips 60 may still remain attached when current is turned off due to the residual field.

The embodiment shown in FIG. 8A is an electromagnet with a magnetic offset—created by winding a coil 58 on a magnet 54. FIG. 8C is an electromagnet including a coil 58 wrapping a core 82 made two components in series a ferromagnetic core 76 and a permanent magnet 54. In alternate embodiments, the coil 58 can be wrapped around the ferromagnetic core 76, the permanent magnet 54, or both. All these active conductor members can have the ability to control the collection of chips 60.

An interesting feature of using a hybrid design is that the coil 58 can be used to potentially cancel out, or lower, the magnetic field of the permanent magnet 54. Accordingly, a chip detector 40 using a hybrid design as an electromagnet can be used in accordance with one or the other of the methods presented above, by activating the coil 58 to reduce, cancel, or even potentially reverse the permanent magnet 54 magnetic field rather than activating a coil 58 to generate a field around a non-magnetic core. The former fails to a permanent magnetic field, whereas the latter fails to a potentially nil or weak magnetic field. Accordingly, the former may be preferred to allow the chip detector 40 to maintain its functionality in the event of a failure of the coil 58 or of the coil's power system.

An example chip detector 40 using two magnetic conductors members based on a hybrid design based on FIG. 8A is presented in FIG. 9. Example states achievable with such a chip detector are presented in Table 4, below:

TABLE 4 example states achievable with two hybrid active/passive magnetic field conductor members Probe 1 Probe 1 Probe 2 Probe 2 Function Current Field current Field Effect Chip Off N-S Off S-N Attract chips between Detector prongs (Opposite field) OFF Positive Nil or Positive Nil or Attracted chips weakly (-Hci) residual (-Hci) residual attached or fall off N-S S-N One Positive Nil or Off S-N Small chips on Probe Off (-Hci) residual deactivated probe fall N-S off. Opposing Positive+ N-S (may Off S-N Small chips bridging (Similar demagnetize) the gap repel each field) other and break the gap Reverse Positive+ S-N (may Positive+ N-S (may Fields are reversed demagnetize) demagnetize) but oppose each other

Hybrid electro-permanent magnetic prongs can attract ferromagnetic chips 60 even when there is no current 59 applied to the coil 58. The magnetic attraction can be increased if power is applied and produces a field in the same direction as the permanent magnet and if the electromagnet is not yet saturated. The magnetic field can be reduced, eliminated or reversed if the field produced by the current 59 is acting opposite to the permanent magnet 54 field. It's important to note that applying a magnetic field H in excess of −Hci in the reverse orientation may lead to demagnetization of the permanent magnet 54. It may therefore be preferred, in one embodiment, to avoid applying current 59 in a manner to cause the H field to drop below −Hci. FIG. 10 represents an example hysteresis loop 86, or magnetization and demagnetization curve, and reference can be made to this curve 86 to illustrate this principle (see arrows). Indeed, a permanent electromagnetic field can be applied, or removed, from a ferromagnetic material by the application of an magnetic field.

Referring back to FIG. 9, such a design can be considered a six pin, two coil, independent electro-permanent magnetic prong design. The actively controlled chip detector 40 can have two permanent-magnets 54; each one having a control coil 58 wound around it to increase, reduce, eliminate or reverse its magnetic field by varying the applied current 59. Each coil 58 is wrapped around a permanent magnet 54 prong to form two electrically controlled permanent magnet prongs. Each electro permanent magnet 84 a, 84 b is activated independently. Like traditional chip detectors, one permanent magnet prong is oriented in a North-South orientation, while the other is oriented in a South-North orientation. However, an independent coil 58 is wrapped around each permanent magnet 54 in such a way that when the coil 58 currents 59 are activated, they weaken the magnetic field of the associated permanent magnet 54. As ferromagnetic debris is collected between the prongs, the measured impedance will change resulting in a chip indication. When the engine is shutoff, any collected debris will remain attracted to the prongs because the field of the permanent magnet 54 field can remain very active. An alternate embodiment can use one hybrid prong and one permanent magnet prong, and still another embodiment can use hybrid prongs having coils interconnected in series on a same circuit, for instance. The hybrid prongs can alternately be as presented in FIG. 8C, for instance.

In an embodiment having two hybrid prongs surrounded by coils 58 connected inversely in series, the coil 58 can be wound in opposite directions such that current 59 applied to IN+ & IN− generates fields that oppose each of the permanent magnet 54 magnetic fields, thus weakening fields of both permanent magnets 54 simultaneously. The number of turns may be different between each prong such that applied current 59 can weaken one permanent magnet prong faster than the other. This strategy can allow one prong to have a reversed field before the other prong's field is turned off. If one permanent magnet prong has more turns than the other, then the current 59 applied to create a field in the reverse direction can cause the field in the permanent magnet 54 with higher turns to reach zero (at −Hci) first before the field in the other permanent magnet 54 (with less turns) does. This unbalance of turns can allow one prong to lose attraction before the other prong does, which can be harnessed to avoid losing a large chip 60 if an alternating sequence is applied such as exemplified above.

A further embodiment is presented in FIG. 11, which can allow example states presented in Table 5, below:

TABLE 5 example states for additional embodiment of FIG. 11 Probe Probe 1 Probe 2 Function Current Field Field Effect Chip Detector Low Low Reduced Attract chips between prongs. (Opposite Positive N-S S-N Both fields are low. The EM is field) low and the PM is reduced. Probe 1 OFF OFF Nil or S-N Chips attracted to probe 2 only. residual Small chips originally attached to N-S probe 1 fall off. Large chips bridging the gap stay attracted to probe 2. Probe 2 OFF Positive N-S Nil or Chips attracted to probe 1 only. residual Small chips originally attached to S-N probe 2 fall off. Large chips bridging the gap stay attracted to probe 1. Opposing Positive+ High N-S Low N-S Fields oppose each other. Probe (Similar field) (may 2 field is lower than probe 1 demagnetize)

The embodiment of FIG. 11 shows a 4 pin chip detector design with a single coil wrapped around a ferromagnetic core and a permanent magnet in series (or PM in series with ferromagnetic core as shown in FIG. 1C) to form an electromagnetic prong and an electrically controlled permanent magnet prong, forming an actively controlled chip detector comprised of an electromagnet and a permanent magnet. Both magnetic conductor members (prongs/disks) share a coil wound around each one sequentially to control the magnetic field strength and direction of the electromagnet and to increase, reduce, eliminate or reverse the permanent magnet's field by varying the applied current. The coil can be wound around the ferromagnetic core and the Permanent magnet in such a way that at max current, the electromagnet produces a field opposite of the permanent magnet, while the permanent magnet field is significantly reduced or cancelled. In one operating mode for this chip detector, the current can be applied around half way, such that both the electromagnet and PM have fields opposing each other.

A further embodiment is presented in FIG. 12, which can allow example states presented in Table 6, below:

TABLE 6 example states for additional embodiment of FIG. 12 Probe 2 Probe 1 Probe 2 Probe 3 Function Current Field Field Field Effect Chip Detector Positive S-N N-S S-N Attract chips between prongs. (Opposite field) Probe 2 OFF OFF S-N Nil or S-N Chips strongly attached to residual probe 1 & 3, and weakly N-S attached to Probe 2. Large chips bridging the gaps are still attracted because probes 1 & 3 are active. Small chips bridging the gap are shed Opposing Negative S-N S-N S-N Small chips bridging the gap (Similar field) repel each other and break the gap

The embodiment shown in FIG. 12 can be embodied as a 4 pin chip detector design consisting of two permanent magnet prongs 90 a, 90 b and an electromagnetic prong 92. A single coil 58 wrapped around one ferromagnetic core 76 can be used to form an electromagnetic prong 92. This actively controlled chip detector comprises three magnets; one electromagnet 56 in between and two permanent magnets 54; the electromagnet 56 having a control coil 58 wound around it to control its magnetic field strength and direction by varying the applied current 59. The permanent magnets 54 are electrically connected to a detection circuit 52 that is activated when a chip 60 bridges both gaps 48 between them.

When the electromagnet 56 is activated, it generates a field opposite that of the permanent magnet prongs 92. Similar to traditional chip detectors, a voltage or current is applied to IND+ & IND− and the impedance between these points is measured. As ferromagnetic debris is collected between all three prongs 90 a, 90 b, 92, the measured impedance will change resulting in a chip 60 indication.

Once the sequence has been exercised once or multiple times, the control system can monitor the resistance again to determine if a chip detection is confirmed. If the resistance is low, it indicates that the collected chip is large and that action should be taken. If the resistance is high, it indicates that the original chips detected were below a certain negligible size. The control system can log both scenarios.

It will be noted that in embodiments using an active electromagnetic conductor member, the electromagnetic conductor member may not have any significant magnetic field when current is not circulating in the coil, and thus not have the capacity to retain particle or chips which had been attracted and retained during chip detector operation, let alone attracting particles not already in contact with the conductor member. A scenario where no electricity circulates in the coil occurs, for instance, when the engine is shut down. In cases where it is further desired for attracted chips or particles to be retained by the chip detector when no current is circulating in the coil, which can be the case in view of sampling during maintenance for instance, this can be an inconvenience of using an active conductor member design over a permanent magnet design. To overcome the latter inconvenience, it can be desired to design the system in a manner to impart a magnetic field into the ferromagnetic core. Indeed, referring to the hysteresis magnetization curve shown in FIG. 10, it will be understood that applying a magnetic field H in excess of the coercivity value of the specific material (Hs) by circulating electrical current along the coil can result in imparting a permanent magnetic field, or more specifically, a saturation remanence (Br) to the ferromagnetic core.

In one embodiment, it can be desired to design the system in a manner that such an active electromagnetic field in excess of Hs be applied automatically, and sporadically, as part of a shutdown sequence. This can further be automated in a manner for the active electromagnetic field in excess of Hs to be applied at shutdown contingent upon confirmation of chip detection, for instance, in a manner for the permanent magnetic field to be imparted only if chip detection has been confirmed, following one or the other of the confirmation methods presented above. In this manner, any accumulated fuzz can be allowed to be flushed at shutdown while chips can be retained for further inspection. In other embodiments, it can be preferred to activate an active electromagnetic field in excess of Hs automatically at shutdown, irrespective of whether a chip has been detected, confirmed, or not detected.

In one example embodiment where the current (e.g. 110, FIG. 6) is varied regularly in the active conductor member within a first amplitude, during magnetic chip detection operation mode of the magnetic chip detector, such as illustrated in FIG. 6 for example, the amplitude of the electrical current pulse circulated in the coil above Hs to impart the magnetic field to retain the particles can be at a second amplitude (e.g. 114). The second amplitude 114 can be higher, at least twice higher, or significantly higher than the first amplitude, to name three examples, particularly in a scenario where the first amplitude 112 is below Hs.

In another example embodiment, the current is varied regularly in the active conductor member within a first amplitude 112 which is above Hs, during operation of the magnetic chip detector, such as illustrated in FIG. 6. In this other example, instead of using a distinct electrical current pulse to impart the magnetic field into the core's material, the moment at which the electrical current is interrupted during engine shutdown can simply be controlled in a manner to coincide with a moment of maximum amplitude of the current (e.g. moment 116), or a moment of maximum intrinsic magnetization of the ferromagnetic core, at which point the current can be interrupted suddenly, with an aim to avoid a scenario where a partial-amplitude magnetic field applied in the opposite orientation would reduce the strength of the intrinsic magnetization of the ferromagnetic core. If the coil is controlled in a manner akin to a square wave, for instance, the current can be interrupted at a suitable moment, i.e. during a period where the wave is at its desired peak, and before the current is reversed, for instance.

The strength of the permanent magnetic field imparted actively by generating an electromagnetic field above the coercivity value of the specific material (Hs) can vary from one application to another. In some embodiments, it can be significantly lesser than the maximum amplitude of the magnetic field during chip detection operation. Indeed, during chip detection operation, it can be desired to not only retain, but attract, ferromagnetic chips circulating in the vicinity of the detector. Attracting ferromagnetic chips can require a much stronger magnetic field than simply retaining chips or fuzz which have already been attracted and which are already within the grasp of the magnetic field of the corresponding conductor member. Accordingly, the strength of the permanent magnetic field imparted in view of retaining any attracted chips can be lesser than, lesser than half of, or significantly lesser than the maximum amplitude of the active electromagnetic field during chip detection operation of the metallic chip detector.

In some embodiments, it can be preferred to apply an electromagnetic field in excess of Hs even in a scenario where the ferromagnetic core is a hard ferromagnetic material with a permanent magnet field. Indeed, in some cases, applying varying currents such as shown in FIG. 6, for instance, to a hybrid conductor member such as one as shown in FIG. 8A or 8C for instance, can affect the strength of the intrinsic magnetic field, and it can be preferred, in some embodiments, to “refresh” the magnetization regularly or sporadically, by applying an active electromagnetic field in excess of Hs. In some embodiments, it can be preferred to refresh the magnetization of the hard ferromagnetic material at each engine mission, such as automatically at engine shutdown or at engine startup for instance. In other embodiments, it can be preferred to refresh the magnetization of the hard ferromagnetic material regularly, such as at specific time intervals for instance, or sporadically, such as by executing a procedure as part of engine maintenance, to name yet another example.

The value of Hs can vary depending on the material. Hard ferromagnetic materials typically have an Hs value significantly higher than the Hs value of soft ferromagnetic materials, and are thus harder to magnetize, but also better at retaining their magnetic field against external electromagnetic influences. In an embodiment such as shown in FIG. 8C, where the core has a magnetized, hard ferromagnetic portion, and a soft ferromagnetic portion, it can be desired, in some embodiments, to allow imparting a permanent magnetic field into the soft ferromagnetic material of the soft ferromagnetic portion, without affecting the existing magnetic field in the hard ferromagnetic portion. This can be done by applying an electromagnetic field above the Hs value of the soft ferromagnetic material of the soft ferromagnetic portion 76, but below the Hs value of the hard ferromagnetic material of the hard ferromagnetic portion 54, for instance.

The current circulated to impart a magnetized state in the core can be in the form of a current pulse. To this end, in one embodiment, a capacitor can be charged during engine operation and magnetic chip detection operation of the magnetic chip detector, and this capacitor can be discharged at the time when the generation of the magnetic state has been determined to occur, such as as part of a shutdown sequence, for instance. FIG. 13 shows one possible embodiment implementing such a capacitor 92. During magnetic chip detection operation, a switch 94 opens the electrical circuit between the coil and the capacitor, and the capacitor is charged by a voltage boost 96 source. To generate the current pulse, the switch is closed, which allows the capacitor to discharge through the coil. In this specific embodiment, current is prevented from returning back through undesired regions of the circuit when the capacitor is discharged. It will be understood that using a capacitor is only one example, and that other ways of generating a current pulse can be used.

Moreover, in some scenarios where no chips are detected throughout the mission, an optional procedure can be to positively clear all the fuzz off the tips of the chip detectors, by turning off the fields or reversing them slightly (to eliminate residual force) prior to shut down. This can be applied to embodiments where a permanent magnetic field is imparted when chip detection has been confirmed, in a manner for the system to either proceed to clear all fuzz, or impart a permanent magnetic field, depending on whether or not chip detection has been confirmed during chip detector mode of operation, or to embodiments which are not designed in a manner to impart a permanent magnetic field during use.

The embodiments described in this document provide non-limiting examples of possible implementations of the present technology. Upon review of the present disclosure, a person of ordinary skill in the art will recognize that changes may be made to the embodiments described herein without departing from the scope of the present technology. For example, the chip detectors can use any suitable conductor member designs (permanent magnet, electro-magnet, permanent electro-magnet) to achieve desired result. The number of conductor member may vary from one embodiment to another, and in particular, a plurality of chip detectors can be used side by side, or otherwise on the same engine. The chip detector system can be used for detecting chips in other liquids than oil or lubricants, such as cooling fluid, for instance. Instead of using two conductor members besides one another, such as in the illustrated examples, alternate embodiments can use two conductor members one around another, for instance. Yet further modifications could be implemented by a person of ordinary skill in the art in view of the present disclosure, which modifications would be within the scope of the present technology. 

The invention claimed is:
 1. A method of operating a magnetic chip detector system integrated within a gas turbine engine, the magnetic chip detector system having a first conductor member and a second conductor member both exposed to a liquid flow path of the gas turbine engine, at least a first one of the conductor members including an electromagnet including a coil wrapped around a ferromagnetic core, the method comprising: performing an engine shutdown procedure including increasing an intrinsic magnetic field strength within the ferromagnetic core including circulating electrical current in the coil; and interrupting the electrical current circulation in the coil for an engine shut-down period of time during which the intrinsic magnetic field strength remains in the ferromagnetic core.
 2. The method of claim 1, further comprising the intrinsic magnetic field retains ferromagnetic particles previously collected by the magnetic chip detector into contact with the corresponding conductor member during the period of time.
 3. The method of claim 1 wherein the ferromagnetic core is a soft magnetic material.
 4. The method of claim 1 including, prior to said increasing the intrinsic magnetic field strength, regularly increasing and decreasing a current amplitude circulation in the coil within a maximum amplitude, and wherein said interrupting the current circulation includes interrupting the current circulation suddenly at a moment where the current circulation is at said maximum amplitude.
 5. The method of claim 1 wherein said increasing an intrinsic magnetic field strength includes circulating the electrical current in the form of a pulse.
 6. The method of claim 5 further comprising generating the current pulse using a capacitor.
 7. A method of operating a magnetic chip detector system having a first conductor member and a second conductor member both exposed to a liquid flow path and separated from one another by gap, each one of the conductor members having a magnetic field oriented into the liquid flow path, at least a first one of the conductor members including an electromagnet including a coil wrapped around a ferromagnetic core in a manner for the corresponding magnetic field to be actively modifiable via control of electrical current in the coil; an electrical energy source configured to induce a current circulation across the gap; and a meter configured to measure a response of the gap to the induced current circulation, the method comprising: increasing an intrinsic magnetic field strength within the ferromagnetic core including circulating electrical current in the coil; and interrupting the electrical current circulation in the coil for a period of time during which the intrinsic magnetic field strength remains in the ferromagnetic core.
 8. The method of claim 7, further comprising the intrinsic magnetic field retains ferromagnetic particles previously collected by the magnetic chip detector into contact with the corresponding conductor member during the period of time.
 9. The method of claim 7 wherein the magnetic chip detector system is integrated into a gas turbine engine, and wherein the period of time corresponds to a period of time during which the gas turbine engine is shut down.
 10. The method of claim 7 wherein said method is performed automatically upon shutting down the magnetic chip detector system.
 11. The method of claim 7 wherein said method is triggered during a maintenance operation.
 12. The method of claim 7 wherein the ferromagnetic core is a soft magnetic material.
 13. The method of claim 7 wherein the ferromagnetic core is a hard magnetic material.
 14. The method of claim 7 including, prior to said increasing the intrinsic magnetic field strength, regularly increasing and decreasing a current amplitude circulation in the coil within a maximum amplitude, and wherein said interrupting the current circulation includes interrupting the current circulation suddenly at a moment where the current circulation is at maximum amplitude.
 15. The method of claim 7 wherein said increasing an intrinsic magnetic field strength includes circulating the electrical current in the form of a pulse.
 16. The method of claim 15 further comprising generating the current pulse using a capacitor.
 17. The method of claim 7, further comprising, prior to said increasing the intrinsic magnetic field strength, and in sequence: generating a magnetic field in a first orientation around at least the second conductor member, while the first conductor member and the second conductor member separated from one another by a gap exposed to a flow of the lubricant, the conductor members forming part of an electrical circuit including the lubricant flow area across the gap; increasing a strength of a magnetic field in a second orientation, opposite the first orientation, around the first conductor member; inducing an electric current across the circuit, and measuring a response of the circuit to the induced electric current; and providing an indication of presence or absence of ferromagnetic chip in the lubricant based on the measured response of the circuit.
 18. The method of claim 17 wherein the period of time corresponds to a period of time during which the magnetic chip detector is shut down, wherein the step of increasing the intrinsic magnetic field is performed contingent upon an indication of said presence of ferromagnetic chip.
 19. The method of claim 18 wherein, upon an indication of absence of ferromagnetic chip, the intrinsic magnetic field strength within the ferromagnetic core is controlled in a manner to avoid retaining previously attracted ferromagnetic particles during said period. 